Characterization of the Static Disorder in the B850 Band of LH2

A systematic simulation study, guided by the expressions of the first-order perturbation theory, was performed for a model of the B850 band in the light harvesting complex 2 of purple bacteria. General types of Gaussian disorder, which include diagonal, off-diagonal, coexisting but independent diagonal and off-diagonal, and correlated diagonal and off-diagonal disorder, were considered. The effects of these types of disorder were studied by calculating four quantities that characterize the energy distribution of the three lowest levels, varying the magnitude of the disorder. For all the cases considered, except for one of the correlated disorder models, a common scaling relation was found among the four quantities, which is in reasonable agreement with available low temperature experimental data. On the basis of this fact and further physical reasoning, it is concluded that the disorder in the B850 is likely Gaussian and that comparable magnitudes of both diagonal and off-diagonal disorder coexist. Three ...